Respiratory Event Scoring

1. Apnea, hypopnea, and RERA: definitions and sensors

A respiratory event is any scored disruption of breathing during sleep. An apnea is a near-complete cessation of airflow (≥90% reduction from baseline) lasting at least 10 seconds in adults; it is detected with the oronasal thermal sensor, which senses temperature change from expired air. A hypopnea is a partial reduction of airflow (≥30% from baseline) lasting at least 10 seconds, associated with either oxygen desaturation or an arousal; it is detected primarily with the nasal pressure transducer, which reflects airflow shape and detects subtle airflow reduction and flow limitation. A RERA (respiratory effort-related arousal) is a sequence of breaths with progressively increasing respiratory effort or inspiratory flattening that terminates in an arousal but does not meet apnea or hypopnea criteria. Event duration is measured from the point of airflow reduction until it returns toward baseline.

2. Obstructive, central, and mixed apnea

Classification depends on the respiratory effort signal (usually from RIP belts on the chest and abdomen):

• Obstructive apnea: airflow is absent or nearly absent, but respiratory effort continues (and often increases) throughout the event—the airway is closed but the patient keeps trying to breathe.
• Central apnea: airflow is absent and respiratory effort is absent—there is no breathing attempt.
• Mixed apnea: the event begins with a central component (no effort) and transitions to an obstructive component (effort resumes while airflow remains absent).

The technologist documents effort presence/absence objectively; the pattern's clinical meaning is the physician's interpretation.

3. Hypopnea rule variations, Cheyne-Stokes respiration, and baseline breathing

Adult hypopnea scoring has documented variations. AASM Rule 1A scores a hypopnea as ≥30% airflow reduction with an oxygen desaturation (commonly ≥3% or ≥4%, depending on the accepted criterion); AASM Rule 1B scores ≥30% airflow reduction with an arousal-linked event (an associated arousal). Because these definitions change the resulting apnea-hypopnea index, the technologist must note which rule was applied. Cheyne-Stokes respiration is a distinctive crescendo-decrescendo pattern—breathing waxes and wanes in a smooth rise-and-fall—punctuated by central events (central apneas or hypopneas), most often seen in the context of heart failure; its central events are scored like any other but must be distinguished by their waxing-waning context. All event scoring depends on establishing baseline breathing, the patient's stable airflow and effort level against which reductions are measured.

4. Hypoventilation, CO2 monitoring, and pediatric differences

Sleep-related hypoventilation is sustained inadequate ventilation during sleep, reflected by elevated carbon dioxide; it is recognized with CO2 monitoring (transcutaneous or end-tidal CO2) rather than by counting apneas and hypopneas alone. Pediatric scoring differences are important: because children breathe faster, event duration is often measured in breaths (for example, a respiratory event lasting at least two breaths) rather than a fixed 10 seconds, and desaturation thresholds may differ. The technologist must apply the age-appropriate rule set and verify against the current AASM manual.

How it works

1. The technologist establishes baseline breathing during stable sleep.
2. Airflow signals (thermal and nasal pressure) are reviewed for reductions lasting at least the required duration.
3. Each apnea is typed by the effort signal; each hypopnea is matched to the applicable rule (desaturation or arousal).
4. Crescendo-decrescendo and central-event patterns, RERAs, and CO2/ventilation findings are documented.
5. Events are tabulated into indices (AHI/RDI), and the technologist flags anything unusual for the interpreting physician.

Common confusions

Memory aids

"T-P-E: Thermal for Apnea, Pressure for Hypopnea, Effort decides the type." Use the thermal sensor for apneas, the nasal pressure for hypopneas/RERAs, and always check the effort belts to call an event obstructive (effort on), central (effort off), or mixed (off then on).

Quick review

Topic Recap

Respiratory scoring identifies apneas (≥90% airflow drop, thermal sensor), hypopneas (≥30% drop with desaturation [1A] or arousal [1B], nasal pressure), and RERAs (effort/flattening ending in arousal). Effort classifies events as obstructive, central, or mixed. Cheyne-Stokes respiration shows crescendo-decrescendo breathing with central events; hypoventilation is recognized by CO2 monitoring; pediatric rules use breath-based durations. The technologist scores and documents, verifies against the current manual, and leaves diagnosis to the physician.

Knowledge Check

1. Which sensor is preferred for scoring apneas, and why?
2. What is the key difference between an obstructive and a central apnea?
3. Under AASM Rule 1B, what qualifies a ≥30% airflow reduction as a hypopnea?
4. What breathing pattern characterizes Cheyne-Stokes respiration?
5. How are pediatric respiratory event durations often measured?

Answers and Rationales

1. The oronasal thermal sensor, because it reliably detects the near-absence of airflow that defines an apnea. Rationale: temperature signal is the standard for apnea scoring.
2. Respiratory effort: obstructive apnea has continued effort, central apnea has no effort. Rationale: the effort signal determines event type.
3. An associated arousal. Rationale: Rule 1B scores hypopnea by arousal rather than desaturation.
4. A crescendo-decrescendo (waxing and waning) pattern with central apneas or hypopneas. Rationale: this smooth rise-and-fall is the signature of Cheyne-Stokes respiration.
5. In breaths (commonly at least two breaths) rather than a fixed 10 seconds. Rationale: children's faster breathing makes breath-based duration more appropriate.